1. Field of the Invention
The present invention relates generally to an undershirt that is worn in a state of being substantially in close contact with a surface of an upper body of a wearer, and particularly to a baseball undershirt that facilitates a pitching motion and a batting motion.
2. Related Background Art
Conventionally, regarding fabrics for use in baseball undershirts, the following fabric configurations have been proposed:                (1) torso pieces are formed with a fabric containing cotton as a main component, and sleeves are formed with a 100% acryl fabric;        (2) both of torso pieces and sleeves are formed with a fabric having an outside surface made of polyester filaments and a body-side surface made of cotton and polyester filaments, both of the outside surface and the body-side surface of the fabric being treated so as to absorb sweat;        (3) both of torso pieces and sleeves are formed with a 100% polyester filament fabric, and are treated so as to absorb sweat.        
The foregoing various types of conventional undershirts are formed with fabrics having a certain stretchability and a high sweat-absorbing property. Such an undershirt has a shape with a relatively great allowance, thereby being shaped so as not to be fitted tightly to, or not to be in contact with, the skin of a wearer, and is composed of roughly four parts of a front torso piece, a back torso piece, and sleeves. Though undershirts have differences in shape depending on purposes of use, such as short-sleeved, long-sleeved, high-necked, and turtle-necked, their functions center on the comfort to the wearers when the undershirts are worn, such as sweat absorption and heat retention during or after playing sports.
Among those, there are some types of undershirts employing light and stretchable materials for forming the entirety or a part of each undershirt so as to improve the motor functionality of a wearer. For instance, undershirts employing a highly stretchable material for sleeve and shoulder parts so as to facilitate the swing of arms are available. However, they simply facilitate the motions, and they are not intended to intentionally assist the wearer's motions.
Further, Japanese Patent No. 3115816 discloses a stretchable shirt for protecting the shoulder and upper arm of a wearer. The shirt has, on the back side thereof, members having a strong straining force, each of which extends from the vicinity of an acromial-side end of an upper portion of the musculus trapezius, through the vicinity of the angulus superior scapulae and the vicinity of any one of the seventh to ninth vertebrae thoracicae, to the vicinity of a lower portion of the costae on the opposite side. The shirt also has, on the front side thereof, members having a strong straining force, each of which extends from the vicinity of a position corresponding to a distal portion of the musculus deltoideus through the vicinity of an edge of a portion corresponding to the musculus deltoideus, and terminates in the vicinity of an upper end of the shirt in the vicinity of an edge portion of a neck opening slightly on a lateral side. Furthermore, the shirt also has, on the back side thereof, a member having a strong straining force that extends from the vicinity of a position corresponding to a distal portion of the musculus deltoideus through the vicinity of an edge of a portion corresponding to the musculus deltoideus, to between a portion corresponding to the vertebra prominens and a portion corresponding to the third vertebra thoracica, and from this portion, extends toward the opposite side so as to be symmetrical between the right and left sides.
This is a shirt that strongly supports muscles and bones that are involved when an injury occurs to the shoulder joint or the muscles in the vicinity of the same, that is effective for preventing such an injury or promoting medical treatments for the injury, that can be worn properly and easily by an amateur, and that provides an effect that is comparable to athletic tape. When a baseball pitcher or the like wears the shirt, such effects can be achieved.
Most of the foregoing conventional baseball undershirts have designs that are driven by wearer comfort. Thus, those shirts focus on features such as sweat absorption and heat retention during or after playing sports. Even if the above shirts are intended allegedly to improve the motor functionality, they only rely on the lightness and stretchability of the fabrics used therein, and are not intended to intentionally assist the wearer's motor functionality. Furthermore, the invention proposed by JP 3115816 simply is effective for the prevention of injuries of the joints and muscles and the promotion of medical treatment, and does not have a purpose of intentionally improving motions of the arms and shoulders during pitching, batting, etc. Therefore, there is a need for a baseball undershirt that has a function of intentionally improving the shoulder and arm movement of a baseball player during pitching and batting so that power is more efficiently transferred to the ball or bat.